Reducing the uncertainty in the forest volume-to-biomass relationship built from limited field plots

1. The method of biomass estimation based on a volume-to-biomass relationship has been applied in estimating forest biomass conventionally through the mean volume (m 3 ha-1). However, few studies have been reported concerning the verification of the volume-biomass equations regressed using field data. The possible bias may result from the volume measurements and extrapolations from sample plots to stands or a unit area. This paper addresses (i) how to verify the volume-biomass equations, and (ii) how to reduce the bias while building these equations. 2. The volume-biomass equations are re-expressed by two parametric equations. The stem biomass plays the parameter's role in the parametric equations, of which one is established by regressing the relationship between stem biomass and volume, and the other is created by regressing the stem allometric equation. The graphical representation of parametric equations proposes a concept of " restricted zone " , which helps to verify the volume-biomass equations in regression analyses of field data. 3. The regressions of the parametric equations are verified for 30 species and forest types corresponding to the three datasets. This study demonstrates that most species, widely distributed in cold, temperate, and subtropical zones, is consistent with the allometric curves. The wood density impacts parameters of volume-biomass equations more than the stem allometric curve does. Our analyses suggest that the averaged allometric equations and specified wood density could be an alternative solution for building volume-biomass equations for those species not yet having field 3 biomass measurements. All these analyses and calculations are based on field measurements from three large datasets for both volume and forest biomass (total 10,840 stands), and one for wood density (16,468 estimates). 4．This paper presents an applicable method for verifying the field data using reasonable wood densities, restricting the error in field data processing based on limited field plots, and achieving a better understanding of the uncertainty in building those equations. The verified and improved volume-biomass equations are more reliable and will help to estimate forest carbon sequestration and carbon balance at any large scale.